Since a miniaturization and performance enhancement of an electronic device has advanced and it becomes possible to carry and use easily the electronic device, there is a requirement for an environment that makes communication possible by connecting a terminal to a network at a place where a necessity occurs. As one of such environments, a development of a network that is temporarily established whenever necessary, specifically wireless ad hoc network technology, has been progressed. In this wireless ad hoc network, a specific access point is not provided and each terminal (for example, computer, handheld information terminal (PDA: Personal Digital Assistance), mobile phone unit, and the like) is autonomously distributed and mutually connected.
In this wireless ad hoc network, since a change in topology frequently occurs differently from a conventional fixed network, it is necessary to establish a route control method for securing reliability, specifically a routing protocol. The routing protocol of the wireless ad hoc network which has been proposed presently is roughly classified into two categories that are an on-demand method and a table drive method. In addition, a hybrid method integrating these two methods has also been proposed.
The table drive method and the hybrid method are said to be comparatively failure-resistant since route information is always exchanged. On the other hand, a size of an overhead due to constant transmission and reception of the information becomes a problem. For example, it is inconvenient to always exchange the route information from a view point of power consumption when considering an environment in which a mobile device driven by a battery is connected to a wireless ad hoc network. In addition, there is also such a problem that it is not possible to cope with a sudden failure when a cycle of updating a route table is long.
On the other hand, in case of the on-demand method, a route is formed by transmitting a route discovery request immediately before starting communication, and therefore even when a failure suddenly occurs in a link at a stage where the communication starts, a valid route is formed disregarding that link. However, when the quality of the link being used deteriorates during the communication such that the route becomes not usable, the communication is immediately interrupted and it is necessary to form a route from a transmission source once again.
As a typical routing protocol of the on-demand method, there is an AODV (Ad hoc On-demand Distance Vector) protocol which is proposed by the MANET WG (Mobile Ad hoc NETwork Working Group) of IETF (Internet Engineering Task Force), for example. In this AODV protocol, a method has been proposed in which a message requesting a rediscovery of a route is transmitted from nodes at both ends and a route is newly formed by a method called “local repair” when a failure occurs in a link to result in break (for example, refer to Non-patent reference 1).
[Non-Patent Reference 1]
“Ad hoc ON-demand Distance Vector Routing”, Charles E. Perkins, et al., (USA), IETF, Feb. 17, 2003, pp. 23-25, Internet drafts <http://www.ietf.org/internet-drafts/draft-ietf-manet-aodv-13.txt>